Abstract
The location of a remembered reach target can be encoded in egocentric and/or allocentric reference frames. While the differences in the cortical activation of these two representations have previously been identified (Chen et al., 2014; Neggers et al., 2006), differences in the functional organization of brain networks have not been described. It is expected that the size and connectivity of those functional brain networks will differ, reflecting more widespread connectivity between dorsal and ventral brain areas in the allocentric task. Here, we performed a secondary analysis of an event-related fMRI task (Chen et al., 2014), to distinguish human brain networks involved in these two forms of representation. The paradigm consisted of three tasks with identical stimulus display but different instructions: egocentric reach (remember absolute target location), allocentric reach (remember target location relative to a visual landmark), and a non-spatial control, color report (report color of target). The properties of brain networks involved were analyzed using graph theory to derive the major network hubs, the clustering between the nodes, and the efficiency of the network. The allocentric task demonstrated less hubness, lower clustering and increased global efficiency. This connectivity pattern is indicative of increased global connectivity - between dorsal and ventral visuomotor regions. An analysis of the modularity revealed three important brain modules, two dorsal and one ventral. The allocentric task showed higher modularity in the anterior dorsal brain module, whereas the egocentric task showed increased modularity in the posterior dorsal brain module. Connectivity between the dorsal modules and the ventral brain module was highest in the allocentric task. Thus, we show differences in the allocentric task and egocentric in the dorsal visual stream. More anterior areas, including frontal areas could be more important for a rule-based spatial coding, i.e., remembering target position relative to landmark.